1. FIELD OF THE INVENTION
This invention relates to improvements in and concerning a flash smelting furnace for producing matte from a copper or nickel sulfide ore as a smelting intermediate for the corresponding metal.
2. DESCRIPTION OF THE PRIOR ART
The flash smelting furnace which uses a sulfide concentrate as a raw material and which is popularly called a "flash furnace" possesses many advantages as compared with the other smelting furnaces and, on the other hand, suffers from many disadvantages. By way of illustrating, the conventional flash furnace for copper will be described with reference to FIG. 2.
In a flash furnace 1, a powdered concentrate 2 and preheated air 3 are jointly blown into a reaction shaft 5 of the furnace through a concentrate burner 4 at the top of the furnace. Inside the furnace shaft 5, sulfur and iron, which are combustible components of the powdered concentrate 2, react with the hot air 3 and melt themselves. The resulting melt is stored in a settler 6. In the settler 6 which is a reservoir for the melt, the melt is divided by differences in specific gravity into a matte 7, which is a mixture of Cu.sub.2 S and FeS, and a slag 8, consisting mainly of 2FeO.SiO.sub.2. The slag 8 is discharged through a slag discharge outlet 9 and introduced into an electric slag melting furnace 10. In the meantime, the matte 7 is withdrawn via a matte discharge outlet 11 in compliance with the demand from a converter which constitutes itself a next step of operation.
Meanwhile, a hot waste gas 12 from the reaction shaft 5 is advanced through the settler 6 and a uptake 13 and cooled in a boiler 14. The slag 8 which has entered the electric slag cleaning furnace 10 is kept heated with the heat generated by the electricity fed in through electrodes 15 and, when necessary, mixed as with lumps of ore introduced into the electric slag cleaning furnace 10, with the result that the copper component is further sedimented to the furnace bottom and only the residual slag containing a copper component is discharged via an outlet 16.
The conventional flash smelting furnace has entailed many drawbacks as indicated below.
(1) Since the auxiliary fuel is used inside the reaction shaft 5 to make up for insufficient calorific supply, an atmosphere of fairly high temperature is formed inside the reaction shaft 5 by the heat of reaction of the concentrate as the raw material and the heat of combustion of the auxiliary fuel. An attempt at increasing the amount of the concentrate to be treated results in a severe wearing of the lining refractory bricks of the reaction shaft 5 by melting, making it necessary to limit the amount of the concentrate to be forwarded through the concentrate burner 4 and treated per unit time to an extent at which the wearance of the bricks by smelting is tolerable. This wearance of the bricks by smelting closely bears on the thermal load of the reaction shaft. The loss is conspicuously heavy when the thermal load exceeds 350,000 Kcal/m.sup.3.hr. Thus, the thermal load is desired to be not more than 250,000 Kcal/m.sup.3.hr.
An addition to the amount of treatment can be realized by increasing the inside diameter and height of the reaction shaft. Since the reaction shaft consequently has an increased surface area, the heat radiatd is increased and the amount of the auxiliary fuel used in making up for the loss of heat is also increased. Such an addition exclusively to the reaction shaft as described above inevitably exposes the existing flash furnace to considerable difficulties.
As a means of permitting treatment of an increased amount of the concentrate, a method which resorts to an increase in the oxygen content of the preheated air 3 or to an increase in the degree of oxygen enrichment may be conceived. Again in this case, the interior of the reaction shaft 5 suffers formation of an atmosphere of still higher temperature. For the sake of avoiding loss of the lining refractory bricks by melting, the amount of the concentrat to be treated has its own upper limit.
(2) In the concentrate burner 4, the powdery concentrate 2 and the preheated air 3 are blown into the empty space of the reaction shaft 5 and the melt consequently formed falls in drops and separates into the matte and the slag in the settler 6. The waste gas 12 from the flash furnace 1, therefore, contains a large amount of dust. This dust accumulates in the uptake 13, in the part interconnecting the uptake 13 and the boiler 14, and inside the boiler 14 and offers obstacle to the passage of gas.
Since the dust contains valuable metals, it is recovered as in the boiler and the electric static precipitator and returned to the flash furnace 1 as entrained by the concentrate 2 being fed thereto. When the recovered dust which has undergone further oxidation and has been deprived of combustibility is to treated in the concentrate burner 4, the amount of the auxiliary fuel required is increased and the incombustible dust has a high melting point. Thus, the proportion in which the dust is entrained by the waste gas and taken out of the furnace is increased to add to the amount of dust.
(3) An attempt at increasing the amount of the concentrate to be treated in the concentrate burner 4 results in a deviation from the optimum gas flow rate inside the reaction shaft 5. Consequently, the ratio of dust generation described in (2) above is increased. Thus, for the sake of curbing the ratio of dust generation, the amount of the concentrate forwarded through the concentrate burner for treatment has its own upper limit.
(4) The reaction shaft 5 is filled with an oxidative atmosphere. Particularly the low-temperature zone in which the powdery raw material blown in through the concentrate burner 4 has not yet been heated sufficiently to the prescribed level is liable to form magnetite. The magnetite offers various hindrances to the furnace operation. For example, the magnetite increases the viscosity of the slag, impairs the separation of the slag from the matte and brings about an increase in the copper content of the slag. Besides, since the magnetite has a high density, it settles to and accumulates on the hearth, raises the surface of the hearth, and decreases the available volume of the hearth. Further, the magnetite combines itself with other oxide, particulary Cr.sub.2 O.sub.3, and gives rise to a slag of high viscosity as an intermediate layer between the matte and the slag and interferes with the separation of the matte from the slag. The slag of high viscosity mentioned above possesses a high melting point and a high viscidity and, consequently renders the discharge of the slag through the slag outlet 9 difficult.